A polymer PTC element has a property of rapidly increasing in its resistance value in order for example to prevent an electrical apparatus from overheating or causing a trouble due to an excess current, for example, when the temperature of the PTC element exceeds a given critical value, that is, it has a positive temperature coefficient property or a PTC property. Such a critical temperature is referred to as the “trip temperature.”
A substrate, onto which an IC chip is mounted, and which is arranged in an electrical apparatus generally has a radiator plate for dissipating heat to its outside which heat is generated with use of the electric apparatus. In a case where such a substrate reaches an extraordinary high temperature due to some reasons, for example, due to allowing an excess current to flow through the substrate, the dissipation of the heat through the radiator plate may not be sufficient, so that it happens that the radiator plate and thus the substrate reach and remain at an extraordinary high temperature. Thereupon, it has been adopted to attach a ceramic PTC element (for example, POSISTOR (registered trademark) manufactured by Murata Manufacturing Co., Ltd., Japan) to the radiator plate, thereby detecting the temperature of the substrate and indirectly preventing the substrate from reaching an extraordinary high temperature.    Japanese Patent Laid-open Publication No. 04-162701 is a prior patent reference.